Friday morning, members of the sheriff's tactical operations unit would not allow Knowles to enter his office in the Ocoee sheriff's substation on West Story Road.

Sources said investigators were trying to obtain a warrant to search Knowles' office.

Steve Maroney, supervisor of the Orlando FDLE office, said he is conducting a ''criminal investigation'' into whether Knowles violated laws prohibiting secret recording of phone conversations.

''He has been relieved of duty pending the outcome of the investigation,'' Maroney said.

Maroney said sheriff's officials requested that the FDLE help in the investigation.

Sheriff Lawson Lamar was out of town and could not be reached for comment. Undersheriff Larry Schultz would not comment on the case.

Knowles also had no comment. His attorney, William Sheaffer, called the investigation ''low-level political in-fighting at the sheriff's department.'' ''Captain Knowles has not been taping conversations,'' Sheaffer said. ''There is no substance to that allegation whatsoever.''

Sheaffer said Knowles has ''a fine reputation in 22 years in law enforcement.''

Knowles, 44, was hired by Lamar in June 1981 and was promoted from lieutenant to captain last month. He previously worked as a police officer in the Tampa area.

Maroney and sheriff's Cmdr. John Guemple, who also is investigating, would not comment on specifics of the allegations.

However, sources said the investigation was sparked by a complaint from an Orange County electronics expert who said he installed a recording device for Knowles in August 1983.

The man told FDLE investigators that Knowles asked him, through a deputy sheriff, to install the device on Knowles' telephone so he could record conversations with his supervisor, Cmdr. Peter Marcus.

Marcus could not be reached for comment Friday.

Electronics expert Kenneth Pearce told investigators that the device was set up to record on any of the five telephone lines into the substation.

Pearce told investigators that he was angry because Knowles never paid him for the equipment or the installation.